Reinsurance (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Written premiums:
Written premiums, direct	$ 1,829,815	$ 1,787,235
Written premiums, assumed	216,415	192,187
Written premiums, ceded	(336,629)	(314,084)
Total net premiums written	1,709,601	1,665,338
Earned premiums:
Earned premiums, direct	1,723,610	1,674,550
Earned premiums, assumed	188,191	188,866
Earned premiums, ceded	(318,945)	(296,008)
Net premiums earned	1,592,856	1,567,408
Ceded losses and loss expenses incurred	173,046	238,995
Ceded commissions earned	71,017	$ 66,356
Uncollectible reinsurance	$ 1,000		$ 1,000